The present invention is directed to an arrangement which has a substrate on which a planar waveguide is formed and which substrate has a trench-like depression in which an optical waveguide fiber is positioned with the core of the fiber being aligned with the planar waveguide of the substrate. The invention is also directed to a method of forming the arrangement.
U.S. Pat. No. 4,973,133, whose disclosure is incorporated herein by reference thereto and which claims priority from the same German Application 38 33 147 as claimed by European Published Application 0 361 153, discloses a coupling arrangement that has a substrate with a carrying surface on which a planar waveguide is formed and the carrying surface is provided with a trench-like depression for receiving a fiber in a play-free and firm manner to be in alignment with the planar waveguide. In this known arrangement, the trench-like depression and the carrier surface of the substrate forms a guide channel for the fiber, wherein the fiber is held play-free and firmly and for this reason must be adjusted very exactly in advance with reference to the planar waveguide, particularly relative to the longitudinal axis of the planar waveguide. To that end, the position of the planar waveguide or the longitudinal axis thereof must be exactly known both vertically as well as laterally with reference to the carrying surface of the substrate. Over and above this, the guide channel must be exactly dimensioned with reference to the dimensions of the fiber.
The planar waveguide is composed of a first layer of a material having a first refractive index applied on the carrying surface of the substrate, a strip-shaped second layer with a longitudinal axis is arranged on the first layer and is composed of a material having a higher second refractive index in comparison to the first refractive index of the first layer, and then a third layer composed of a material having a refractive index that is lower in comparison to the second refractive index will cover the strip-shaped second layer. The strip-shaped second layer forms the core and the first and third layers form the cladding of the planar waveguide.
In this known arrangement, the substrate, the first layer and the third layer are composed, for example, of InP and the strip-shaped second layer is composed of a quaternary material, for example of InGaAsP.
An article, by C. H. Henry, G. E. Blonder, R. F. Kazarinov, entitled "Glass Waveguides on Silicon for Hybrid Optical Packaging", Journal of Light Waveguide Technology, Vol. 7, No. 10, October 1989, pp. 1530-1539, discloses that optical circuits for distributing, for receiving, for transmitting or for amplifying optical signals in optical communication technology are often executed in planar technology in doped silica glass (SiO.sub.2) on substrates of Si, for example Si wafers.
A planar waveguide of doped silica glass on a substrate of Si similar to the planar waveguide of the above-mentioned U.S. Patent is known, for example, from an article by H. W. Schneider entitled "Realization of SIO.sub.2 --B.sub.2 O.sub.3 --TIO.sub.2 Waveguides and Reflectors on SI Substrates", Mat. Res. Soc. Symp. Proc., Vol. 244 (1992), pp. 337-342. This waveguide comprises a first layer of SiO.sub.2 doped with B.sub.2 O.sub.3 applied on a carrying surface of a substrate, a strip-shaped second layer of SiO.sub.2 doped with B.sub.2 O.sub.3 and TiO.sub.2 arranged on the first layer, and a third layer of SiO.sub.2 doped with B.sub.2 O.sub.3 that covers the strip-shaped second layer.
The manufacture of this planar waveguide of doped silica glass can, according to the article by Schneider, occur so that the first layer of SiO.sub.2 doped with B.sub.2 O.sub.3 is deposited on the carrying surface of the substrate of Si, and the second layer of SiO.sub.2 doped with B.sub.2 O.sub.3 and TiO.sub.3 is deposited on the first layer. One or more strips of mask layers of amorphous silica are arranged at a distance from one another and are produced on the surface of the second layer. The second layer is etched away outside the strip on the basis of a reactive ion etching method having an etchant that attacks the material of the second layer but not the amorphous silicon, so that one or more strip-shaped raised ridges of the second layer remain on the first layer, and these ridges are covered with the amorphous silicon. The amorphous silicon is removed and the remaining raised ridge or ridges of the material of the second layer are now covered by deposition of a third layer from an SiO.sub.2 doped B.sub.2 O.sub.3. As in the planar waveguide according to the above-mentioned U.S. Patent, each ridge forms a core and the first and third layers form the cladding of the planar waveguide whose longitudinal axis is defined by a longitudinal axis of its strip-shaped ridge composed of the material of the second layer.
Because of the manufacturing conditions, the three doped silica layers produced in this method have thickness fluctuations up to 0.5 .mu.m so that the vertical position of the core of the planar waveguide over the carrying surface of the substrate or, respectively, under the surface of the third layer is poorly defined. The lateral position of the core in the direction parallel to the carrying surface and perpendicular relative to the longitudinal axis is initially also unknown.